LSS-BASIC BLOC WITH WIDE
Setup with 3D printing
download files here: http://www.thingiverse.com/thing:1863766
normaly you need only to adjust the length of rods. Give us your feedback and... enjoy it!
For those who have already built
a block with a 50mm condenser, and did not find suitable projector, here
is a list of compatible Beamers:
some Compatible Projectors (at mars 2020 ) ,
ultra short zoom factor (no rate
Acer H6531 BD
old listing (2016 nov)
Acer P1623 (1200p)
RZ475E / U ( Led )
However, only 2 were tested (February
2014)acer P1500 and benq W1070 . My preference is naturally acer, where
the light leaks are quite low and consistent with the use of the planetarium
(which is not always the case, remember Optoma HD10).
Why a 50 mm F/D=1.4 ?
Because of the size of the rear
lens of the objective, which is often too small. Only the bright optical
lens allows the entire field to be projected.
with a F/D=1.8, the edge of the
field is lost and you lose 10° on the horizon.
If you use a mount lenses (e.g.
CANON or NIKON) beware of the distance between the Fisheye and the condenser.
Depending on the case, it will imply to stick the optical fisheye into
the diagonal a little bit more, contrary to what is presented here, with
a larger space.
Simplified setup without 3D printing
- Peleng 8mm fisheye
- 50 mm objective F/D1.4 with 42
screw mount (here Takumar SMC)
- A 2 inches diagonal (Kepler brand)
- 2 extension tubes 32 mm screw
- 2 adaptor rings: 2 inches outside
(50.8 mm 1/24 inch) / 42 mm inside, 1 mm (metric)
- 1 ring inversion M49 / M42x1
An adjustable setting to center the
diagonal in front of the videoprojector.
A good surprise!
Wanting to equip the planetarium
Bressan with a 2nd projector , I wanted to test some new features. My choice
went to the ACER P1500 , a compact Full HD at 3000 lumens !
But here was a big trouble : this
projector is INCOMPATIBLE with based Heligon blocks! I did not pay attention
to the angle of projection particularly wide ; it is a new generation of
devices requiring a wider condensor for getting a good fit. So I went back
with my old block 50mm based system.
And then, surprise : the projection
angle is perfectly suited ! And the quality is awesome even at horizon.
No need to put diaphragm or any added lens. We tested this block with lionez
Ruiz under the dome of the planetarium Marseille ( 6m). Nothing to say,
the 3000 lumens is perfectly suited for it.
No more need to run after those precious
Heligon 75mm anymore ! Just choose the right projector for the right block.
Now you understand, hunting good
old 50mm is open! (typically between 50 and 58mm). Especially we can find
used and new ones ! For my tests , I used a 50 mm Takumar F/D1.4 (why so
open, see page link), a diagonal 2 inches and a few rings .
The lens is held by a bracket that
holds the wood bent pinch, easily achievable with few tools and a sense
of very rough DIY reference (click the image). The rest is very classic
, wedges to tilt the projector, etc. .
Where to find
the right elements and the right connectors ?
For this block, we need :
-a condenser consisting of a 50 mm
F/D1.4 ( lens size ) , nine Canon USM 50 mm f / d or 1.4 : Used Lens screw
( M42 ) for reasons of rings coupling
-a diagonal ( threaded 2 inch 2 sides
, the case of Kepler and Skywatche "basic" , but not necessarily all other
-Peleng 8mm fisheye one with his
mount M42 screw ( the Samyang is an aspheric and therefore less interesting
because it deforms the projection on the horizon)
for adjustments, here are some details
; Warning they are experimental
a M42 camera lens
a "Canon" camera lens
M : male F: female
T2: 42mm diameter
M42 : 42mm diameter
50.8 mm (2 inches) , not 1/24 "
M48 : 48mm diameter
( internal thread of 2pouces ) not 1/24 "
and the icing on the cake : the
list of supplies (also to validate).
I do not have shares in TS, but
they have everything you need (fast and cheap) :
Yves LHOUMEAU - mars 2020